Effect Of Exogenous Melatonin Treatment On The Black Spot Of Postharvest Apricot Fruit

Apricot is one of the characteristic fruits in Xinjiang.Due to the high harvest temperature in summer,the quality of apricots is easy to deteriorate.Alternaria alternata is easy to cause apricot fruit black spot,which will reduce the quality and commodity value of apricot fruit during storage and transportation.Therefore,‘saimaiti’apricot was treated with exogenous melatonin（MT）and inoculated with A.alternata.Explore the effect of exogenous melatonin on the black spot of apricot fruit,and screen the most effective concentration of exogenous melatonin combined with quality.The resistance of exogenous melatonin treatment to the black spot of postharvest apricot fruit was analyzed from the perspective of active oxygen metabolism,phenylpropane metabolism and cell wall metabolism,combined with the scanning of stomatal structure of apricot fruit by electron microscope,to provide a theoretical basis for the control of exogenous melatonin on postharvest black spot of apricot fruit.The main results are as follows:（1）To explore the effect of exogenous melatonin treatment on postharvest apricot fruit black spot,and screen the most effective concentration combined with quality.The results showed that compared with the control group,50,100,200μmol/L exogenous melatonin treatment could significantly reduce the incidence rate of apricot fruit inoculation,and slow down the development of lesion diameter of apricot fruit,the most effective inhibition was100μmol/L exogenous melatonin treatment group.In addition,melatonin delayed the decrease of hardness,titratable acid,ascorbic acid content and the color turning of apricot fruit.The above research shows that 100μmol/L exogenous melatonin treatment had the best effect on inducing the black spot of apricot fruit and maintaining the quality of apricot fruit during storage.（2）Exogenous melatonin treatment increased SOD enzyme activity and decreased the production rate of superoxide anion（O₂^-·）radical,inhibited CAT enzyme activity and induced rapid accumulation of H₂O₂in apricot fruit in the early stages,significantly enhanced the activity of POD and CAT activity during anaphase storagethe,reduced the accumulation of H₂O₂and MDA content in apricot fruit,and the integrity of cell membrane structure of apricot fruit was kept.Those findings suggested that melatonin could regulate reactive oxygen species metabolism to induces resistance to black spot in postharvest apricot fruits.（3）Exogenous melatonin treatment induced the increase of PAL,C4H,4CL and other enzyme activities during postharvest storage of apricot fruit,promoted the accumulation of total phenols and flavonoids in apricot fruit,increased PPO and CAD enzyme activities,accelerated the accumulation of lignin content in apricot fruit,and significantly enhanced the disease resistance of apricot fruit.The results showed that exogenous melatonin treatment could induce and enhance the resistance of postharvest apricot fruit to black spot by regulating phenylpropane metabolism.（4）Exogenous melatonin treatment increased PME,PG,Cx,β-Gal enzyme activitiesand and delayed the accumulation of WSP and CSP contents in apricot fruit and reduced the decrease of SSP and cellulose contents.Compared with the control group,exogenous melatonin maintained the integrity of apricot fruit stomatal structure and inhibited the mycelial growth of apricot fruit epidermis.The results showed that exogenous melatonin treatment could induce and enhance the resistance of apricot fruit to black spot by regulating cell wall metabolism.All above results showed that exogenous melatonin treatment not only slowed down the decline of apricot fruit quality during storage,but also enhanced the resistance of apricot fruit to black spot by regulating reactive oxygen species metabolism,phenylpropane metabolism and cell wall metabolism induction.